You cannot donate blood when you have a cold, as colds are mostly caused by bacterial or viral infections, and donations are not allowed during this time. Before donating blood, a series of tests are required, and donation is not allowed when you are sick. Additionally, your immune system is generally weaker when you have a cold. Donating blood at this time could worsen the symptoms of the cold. After donating, your immunity could be even lower, making your body weaker, thus hindering the recovery from the cold. Therefore, you should not donate blood while having a cold. Wait until at least half a month after the symptoms have subsided before donating blood. Furthermore, you should eat lightly, avoiding spicy, greasy, raw, or irritating foods. Before donating blood, you should avoid smoking, drinking alcohol, and staying up late to ensure you get enough sleep and boost your immunity.